In the field of radiotherapy treatment, it is often necessary for medical staff, typically a radiation oncologist, to delineate a target volume and tumour within a medical image of a patient for radiotherapy planning. This image is normally a computed tomography (CT) scan, although it may be another imaging modality. It is also necessary for the medical staff, for example a dosimetrist or radiographer, to delineate all normal organs within the medical image, considered organs at risk on the planning image. This is done so that the planning software, which (semi-)automatically calculates a treatment plan, is able to maximise the plan radiotherapy dose to the target volume and tumour, while minimising radiation dose to healthy organs.
The process of delineation is known as contouring. Typically two dimensional (2D) contours are drawn on cross-sectional image slices, although the planning medical image is typically a three dimensional (3D) volumetric image. Therefore the delineation of, say, an organ would consist of a stack of 2D contours, representing a volumetric outline. Contouring can also be performed in 3D using some systems. Since contouring can be both 2D and 3D, the term structure is often used to represent the delineation on the image, whether 2D or 3D. Where the term contour is used, this indicates a single 2D delineation only. For clarity, the term contouring as used herein may indicate the process of delineation in either 2D or 3D to form a structure. Furthermore, the term auto-generated contouring is used herein to indicate a contour or structure produced automatically (as opposed to manually), with the term auto-generated contour or auto-structure referring to such an automatically produced contour/structure.
Manual contouring, as generally performed for radiotherapy contouring is time consuming, and is a significant bottleneck in the treatment planning process, particularly for advanced treatments needing detailed contouring. Therefore, systems have been developed for generating contours, known as auto-generated contouring. Auto-generated contouring can be performed in a number of different ways, for example through the use of previous example cases known as atlases, or through model-based segmentation approaches. However, no current auto-generated contouring systems are perfect, automatically generated contours typically require manual editing to ensure that they delineate the target volume (e.g. organ or tumour) with sufficient accuracy.
To manually contour a spinal cord (without any assistance from an auto-generated contouring system) a radiographer might typically contour, say, every 3rd slice of a CT image and then use contour interpolation to ‘fill in the gaps’ for the remaining slices of the image.
Conversely, when presented with auto-generated contours for all slices of the CT images, the radiographer will have to edit each incorrect slice. Consequently, although time is saved by having an initial set of auto-generated contours for all slices, additional time is spent having to subsequent edit (or at least approve) every slice. Therefore, although auto-generated contouring solutions may reduce the time taken compared to fully manual contouring, they still do not significantly reduce the overall time taken for radiotherapy contouring, and they still require some manual contouring or editing. As such, even with the aid of current auto-generated contouring systems, radiotherapy contouring remains a bottleneck in clinical practice.
Thus, there is a need for a more efficient and less time-consuming approach to radiotherapy contouring.